Volume 7 Issue 2
What’s Happening at Missouri S&T:
Short Course Dates
We will be offering ?Basic Composition of Coatings" March 28-April 1, 2011 (Spring 11). The Basic Composition course is intended for new personnel in the coatings profession. It targets the components of coatings (resin, pigments, extenders, solvents and additives), testing and specifications, general formulation and manufacturing methods. Basic Composition is primarily a lecture course with several laboratory demonstrations.
We will be offering ?Introduction to Paint Formulation" May 9-13, 2011 (Spring 11). This course is intended to give the person a fundamental knowledge of how to approach a starting formulation and troubleshoot it. This course involves both lecture and laboratory work.
We will be offering "Introduction to Coatings Composition and Specifications" July 18-20, 2011 (Summer 11), course designed for the new coatings person in areas such as sales, marketing or production. The course was initiated by a number of raw material companies and distributors requesting a course with this format. This course is not as heavily technical as is our “Basic Composition of Coatings" and “Introduction to Paint Formulation" courses. The ?Introduction to Coatings Composition and Specifications" course is a two and a half day course which will discuss the types of coatings, the basic composition of coatings and the tests and specifications used by the industry. This course will allow the participant to gain the fundamentals needed to work in this industry and to communicate more clearly.
For more information see our web site at http://coatings.mst.edu/index.html and to register contact Catherine Hancock at email@example.com or firstname.lastname@example.org or call 573-341-4419. **These courses are held on the Rolla Campus**
Technical Insights on Coatings Science
Physical Vapor Deposition Aluminum (PVDA): A special class of effect pigments
Ameya Natu, Graduate Research Student, Missouri S&T
There are many different types of effect pigments available in the market. They can be categorized by type; as effect pigments without a layer structure (substrate free pigments), multilayer structures of the Fabry-Perot type pigments, substrate based effect pigments and pigments with structured surfaces. They are also categorized by manufacturing processes as gas phase deposition, liquid phase deposition and casting and extrusion techniques. Gas phase deposition is subcategorized into Chemical Vapor Deposition Process and Physical Vapor Deposition Process (PVD) 1.
PVDA falls under effect pigments without a layer structure (substrate free pigments) and as the name suggest, are manufactured by Physical Vapor Deposition of the aluminum on a substrate. It is also called Vacuum Metalized Pigment (VMP) 1. These pigments have been around for about 30 years but still are considered ‘exotic’ commercial metallic pigments. This is because of their unique mirror effect property. The PVD process provides the pigment with unique characteristics which cannot be achieved with conventional pigment manufacturing processes.
Conventional aluminum pigments are manufactured as cornflake or silver-dollar pigments. These manufacturing process selections not only depend on quality and shape of starting material but also on milling conditions. PVD aluminum is manufactured by a vacuum process. In this process aluminum is deposited as an extremely thin layer on a substrate called web. Web consists of conventional poly-ethylene or PET foil coated with release-coat of acrylates, vinyl resins or cellulosic polymers using gravure or flexographic printing technique2.
Thickness and surface structure of pigment particle can be modulated by various factors such as exposure time, concentration of metal vapors etc. The coated foil is then passed through solvent bath dissolving the release-coat selectively and aluminum film is released as coarse particles. The resulting dispersion of coarse aluminum fragments is concentrated, washed and broken down into aluminum flakes using a high speed stirrer with average particle size of 10 to 12 µm. These thin flakes show improved mirror-like effects when incorporated in coating systems. These flakes are available commercially as 10% or 20% dispersion systems2.
Special characteristics of PVD pigments
- Exceptional luster and reflecting power
- Excellent mirror and chromium-like effects.
- Outstanding non-leafing characteristics because of the absence of lubricants like stearic or oleic acid3.
- Thickness of pigment particle, aspect ratio
- Surface structure of pigment particle2
The aspect ratio of PVDA pigments particles is very high compared to conventional aluminum pigments. Higher aspect ratio gives them higher mobility and hence better leafing effect allowing them to orient parallel to the substrate. This results in maximum specular reflection though the pigment orientation also depends on external factors like surface structure of substrate, formulation parameters and the application technique4.
- Coatings industry: due to the exceptional luster, hiding power and pronounced flop-effect the PVD pigments are increasingly used in industrial paint and automotive finish coatings such as: car interiors, bicycle finishes, mobile phones, watches, and consumer electronics.
- Printing ink industry: PVD pigments are cost-effective alternative to metallized printed articles or foil embossing. They are widely used in label and packaging industries2.
- Better flop effect can be achieved at 3-6% Pigment loading. PVDA flakes get disoriented at higher pigment loading which can deteriorate the metallic effect.
- Poor barrier protection due to application of very thin films
- This technology is expensive compared to others but yields better products5.
The PVD pigments can be used creatively to produce various styling effects in the coated material. They produce exceptional brilliance, hiding power and metallic effects unmatched by other conventional metallic pigments. They can be readily combined with titanium dioxide, pearlescent pigments, transparent pigments, dyestuffs to provide improved optical effects. The state of the technology of deposition equipment and coating materials is well developed, but minor variations continue to improve both.
- Maile, F. J.; Pfaff, G.; Reynders, P.; Progress in Organic Coatings, Volume 54, Issue 3, 2005, Pg 150-163
- Wissling, P. ; Metallic Effect pigments, 2006
- Pfaff, G. ; Special Effect Pigments: technical basis and applications, 2008.
- Poth, U. ; Automotive coatings formulation: chemistry, physics and practices, 2008
- Seubert, D. ; PVD Aluminum Pigments: Superior Brilliance for Coatings & Graphic Arts, Paints and Coating Industry, June 2000